Revert parallel http server

[tpressure]

The multi-threadded HTTP server causes major problem at our customer. There are some situation where we end up in a life-lock. The backtrace in this situation looks like this:

Thread 14 (Thread 0x7fe3f19ca6c0 (LWP 2259726) "http-worker-1"):
#0  syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
#1  0x000056401d6af8b6 in std::sys::sync::mutex::futex::Mutex::lock_contended ()
#2  0x000056401d8ab594 in std::sys::backtrace::__rust_begin_short_backtrace ()
#3  0x000056401d8ad7c8 in core::ops::function::FnOnce::call_once{{vtable.shim}} ()
#4  0x000056401d6b7c5f in std::sys::thread::unix::Thread::new::thread_start ()
#5  0x00007fe3f2067b7b in start_thread (arg=<optimized out>) at ./nptl/pthread_create.c:448
#6  0x00007fe3f20e57b8 in __GI___clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:78

Since we don't need the multi-threadded http server, revert it.

I had some revert conflicts that I needed to resolve, please look closely if I did everything correctly.